FYI, you're right, Gerrit: CCIDs 2 and 3 don't mention CCMPS because for
those CCIDs, CCMPS=\infty. CCID 4, when defined, will impose a CCMPS.
Eddie
Gerrit Renker wrote:
| > | Do we calculate mss anywhere?
| > Yes there is support in dccps_mss_cache .
| > At the begin of dccp_send_msg e.g. it is used.
|
| Yup, look at dccp_sync_mss() used in dccp_connect_init():
<snip>
Thank you for the helpful `pointers' :) - I was amazed a couple of months ago
about how much of that code is active and quietly doing its job with accuracy.
| /*
| * FIXME: this should come from the CCID infrastructure, where,
| * say, TFRC will say it wants TIMESTAMPS, ELAPSED time, etc,
| * for now lets put a rough estimate for NDP + TIMESTAMP +
| * TIMESTAMP_ECHO + ELAPSED TIME + TFRC_OPT_LOSS_EVENT_RATE +
| * TFRC_OPT_RECEIVE_RATE + padding to
| * make it a multiple of 4
| */
|
| mss_now -= ((5 + 6 + 10 + 6 + 6 + 6 + 3) / 4) * 4;
|
I thought that when we are actively using the provided MSS facilities, then there
is more incentive to tackle this one above too.
| Infrastructure wise I guess struct ccid_operations should have a...
| lemme read the relevant part of 4340... there CCMPS:
|
| ----------------- 8< -------------
| 14. Maximum Packet Size
|
| A DCCP implementation MUST maintain the maximum packet size (MPS)
| allowed for each active DCCP session. The MPS is influenced by the
| maximum packet size allowed by the current congestion control
| mechanism (CCMPS), the maximum packet size supported by the path's
| links (PMTU, the Path Maximum Transmission Unit) [RFC1191], and the
| lengths of the IP and DCCP headers.
| ----------------- 8< -------------
I don't know how often I read through 4340, 4341 and 4342 trying to find out what `CCMPS'
is for - it seems that in CCID2 and CCID3 it is both set to `infinity', at least I can
find no explicit mention in 4341/4342 of CCMPS.
But for the MSS caching a `ccid_mps' member would be useful anyway for the above required purpose.
This in turn re-opens other questions - in CCID3 e.g. feedback packets should always contain
also a Loss Intervals option - which is still missing in CCID 3.
It is good that you raise this; I put a copy into my ToDo folder and will ask around in some time
if anyone is working on it. If no one else does it I will give it a try at some time, but am bogged
down by other work. I am re-working the CCID `larger initial windows' patch at the moment, plus
sequence number issues.
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